The aeronautical turbine engines conventionally comprise several modules such as a high pressure compressor, a combustion chamber, a high pressure turbine followed by a low pressure turbine, which drive the corresponding LP or HP compressor, and a gas discharge system. Each of the turbines is formed with one or more stages, each stage successively including a stationary vane impeller or nozzle guides and a moving vane impeller.
Moving vanes are carried at their lower part by the turbine engine rotor and attached to a turbine disc. In contrast, nozzle guide vanes are held by their upper part and attached to a casing, referred to as turbine casing. The terms “lower” and “upper” are to be considered relatively to a distance to the turbine engine axis: the lower part of a piece, when said piece is fitted in the turbine engine, is closer to the turbine engine axis than the upper part of said piece.
With reference to FIG. 1, a turbine casing 10 has, in a longitudinal cross-section, a casing body 11 on which a plurality of rail couples 12 is attached, each rail couple 12 being comprised of an upstream annular rail 13 and of a downstream annular rail 14, each rail couple 12 being intended to hold guide nozzles 15 of a turbine stage. There are thus as many rail couples as turbine stages. The terms “upstream” and “downstream” are to be considered relative to a general direction of flow of fluids through the turbine engine, from upstream to downstream.
The upstream rails 13 each include a plate 16 extending axially (with reference to the axis of rotation of the turbine engine) downstream. On each upper face of the plate 16 of the upstream rail 13, an upstream hook 17 of a nozzle guide is placed, integral with a platform of the nozzle guide 18, which also extends axially upstream. The nozzle guide 18 is carried at its downstream end by the downstream rail 14 associated with the considered upstream rail 13.
After a certain working time, a wear of the upper faces of the plates of the upstream rails is noticed, resulting from micro-displacements created by vibrations and a thermal expansion differences between the upstream rails and upstream hooks. This wear can alter the tilt of nozzle guides which can then tip over around the downstream rails and degrade the engine operation.
Thus, when an upper face of an upstream rail is damaged, it is necessary to repair the rail.
A known repairing method consists in covering the upper face of the rail with a solder by welding, in order to add material, then in machining the covered face. However, this repairing method has a major drawback. The upper face is joined to a concave surface of a highly strained rail portion. A machining springback, that is a geometric discontinuity due to the exit of the machining tool, is therefore forbidden in the concave surface. Indeed, a springback would lead to a significant stress embrittling a highly strained portion. Yet, given the welding accuracy, which is in the order of a few millimetres, the solder may sometimes overflow up to the concave surface. It is thus impossible to suppress this solder, since machining the concave surface would lead to a springback in the concave surface.
Moreover, this repairing method does not enable the concave surface of the rail to be repaired when it is damaged.